Vehicular exhaust systems comprise a complex circuitous array of pipes which carry the heated exhaust gases from the engine to a location where the exhaust gases may safely and conveniently be emitted. Typically, the engine is near the front of the vehicle and the exhaust system terminates near the rear of the vehicle. As a result, the array of pipes comprising the exhaust system must weave its way past other vehicular components. The limited space available both in the engine compartment and under the vehicle necessarily brings the array of exhaust system pipes into very close proximity to other parts of the vehicle, including various electrical components, fluid carrying tubes, the passenger compartment and such.
Government agencies have imposed emissions standards on automobile manufacturers in an attempt to achieve cleaner air. Automobile manufacturers have determined that the levels of certain objectionable components of exhaust gas emissions can be reduced by effecting more complete combustion of the fuels. However, this more complete combustion significantly elevates the temperatures of the exhaust gases directed through the exhaust system of the vehicle. These elevated temperatures can create safety problems or cause structural damage to components of the vehicle near the exhaust system. Consequently, it is necessary to spare and/or insulate at least portions of the heated exhaust system from selected other parts of the vehicle.
Air gap pipes are one extremely effective means for controlling the dissipation of heat from tubular exhaust system components. In particular, the air gap pipe comprises an inner pipe for carrying exhaust gases, and an outer pipe generally concentric with the inner pipe but spaced radially therefrom. The air gap between the inner and outer pipe provides an effective heat insulation and prevents direct contact with the very hot inner pipe. Frequently, the air gap pipe will follow the circuitous non-linear alignment required for the exhaust system as the system extends through the engine compartment and toward the rear of the vehicle.
The prior art has included many methods for manufacturing air gap pipes. The most typical method has included the bending of both the inner and outer pipes into substantially identical non-linear configurations. The outer pipe was then manually fed through a ban saw or the like to cut the outer pipe longitudinally in half. The inner pipe was then disposed between the severed longitudinal halves of the outer pipe, and the outer pipe halves were then rewelded to one another to define an air gap pipe.
Another prior art manufacturing method for creating an air gap pipe has required the placement of a linear outer pipe over a linear inner pipe. The air gap between was then filled with a material having a lower melting point than the metal of either pipe. The inner and outer pipes with the filler therebetween would then be bent into the required circuitous configuration. The assembly of bent pipes would then be heated to a sufficient temperature to enable the filler material to be melted and poured from the gap between the inner and outer pipes. Once again, this manufacturing process was extremely time-consuming and costly.
The prior art has also attempted to employ complex systems of stamp formed heat shields to effectively create an air gap pipe. Heat shield systems such as these are shown in U.S. Pat. No. 3,863,445 which issued to Heath on Feb. 4, 1975.
Particularly effective methods for manufacturing an air gap pipe are shown in U.S. Pat. No. 4,501,302 and U.S. Pat. No. 4,619,292 both of which issued to Jon W. Harwood, and in U.S. Pat. No. 4,656,713 which issued to Bruno A. Rosa, et al. These prior art patents are assigned to the assignee of the subject invention, and the disclosures of these patents are incorporated herein by reference. The methods disclosed in the three previously recited patents involved bending the inner and outer pipes into substantially identical configurations. Supporting means, such as inwardly directed dimples on the outer pipe, are then formed, and the outer pipe is cut longitudinally in half by a preprogrammed robotic cutting apparatus. The outer pipe halves then are clamped around the inner pipe, and the two outer pipe halves are welded together.
Robotic machining and cutting devices are known to follow extremely precise preprogrammed instructions. However, it has been found that metallurgical differences between respective pipes will cause each outer pipe to respond differently to the bending apparatus. As a result, the shape of the pipe presented to the robotic cutting apparatus described in the three previously described patents may vary from the specified shape. Although the variations may be within the limits acceptable for installation of the exhaust system on the vehicle, these variations could result in the robotic cutting device being directed to a significantly off-center location. To account for these possible variations, the system described in U.S. Pat. No. 4,656,713 includes a robotic end effector which is uniquely adapted to follow the actual bent shape of the pipe rather than the specified shape. This is achieved by linear biasing means disposed at angles to one another and operative to follow the actual shape of the pipe. Thus, the end effector will ensure that the circuitously bent outer pipe will be cut substantially precisely longitudinally in half despite significant variations of the bent pipe from its specified configuration. The end effector disclosed in U.S. Pat. No. 4,656,713 is also the subject of a Divisional Application pending an Application Ser. No. 016,648 which was filed on Feb. 19, 1987.
The inventions disclosed in the above described patents and applications have made air gap pipes be an economically feasible option for many complex exhaust system components where temperature levels and heat dissipation are critical. In many of these systems, the space available for the exhaust system components is extremely small, and the exhaust system will pass in very close proximity to other parts of the vehicle. This will often require very sharp bends in the exhaust system components. Additionally, it will often be necessary to cut windows in the outer pipe to bring the exhaust system closer to a structural member that can withstand the higher temperatures of the inner pipe or to provide a vent for dissipating the heated gas within the air gap. In still other situations, a window in an outer pipe will be required to provide room for other structures such as mounting brackets or probes to assess the combustion process. Although the end effector disclosed in U.S. Pat. No. 4,656,713 and in copending Application Ser. No. 016,648 is capable of making the longitudinal cuts along the sharply bent pipes and cutting the above described windows, it is desirable to provide an end effector that can make these complex cuts more efficiently despite variations in the shape of the pipe from its specified shape.
In view of the above, it is an object of the subject invention to provide an end effector to enable complex machining operations in longitudinal members despite variations from one such member to the next.
It is a further object of the subject invention to provide an end effector to enable efficient machining operations on longitudinal members despite geometric and positional variations of the longitudinal members relative to a plurality of different axes.
A further object of the subject invention is to provide a robotic apparatus for making at least longitudinal and circumferential cuts at precise locations in a tubular member that is subject to variance from a specified configuration.
Still a further object of the subject invention is to provide a robotic cutting apparatus for efficiently placing complex non-linear cuts in a tubular member.